Modern autorack cars, which is to say autorack cars built since about 1975 for carrying automobiles, trucks or other vehicles in a multiple deck arrangement, have typically had the structure of a flat car underframe covered by a surface defining a main deck for supporting automotive vehicles. Most typically an upstanding elevated-deck supporting framework is mounted to the underframe. Since about 1975 the framework has usually been enclosed within, or used also to support a barn-like housing structure, which may be referred to as a closure system. Closure systems may include side screens, roof, and end closures, typically in the form of movable doors, the better to discourage thieves and vandals. This superstructure is typically referred to collectively as the “rack” of the autorack. Most typically the framework structure includes a series of vertical posts spaced along the sides of the car, with diagonal bracing or shear web panels between the posts, as may be, and one or two additional decks spaced upwardly from the main deck, and upon which respective second and third layers of automotive vehicles may be transported. That is, the rack may be a bi-level rack (i.e., a single elevated deck spaced upwardly above the main deck of the underframe) or a tri-level rack (two upper decks rather than one). The cars tend to be as tall as permitted under the applicable AAR plate clearance diagrams, for this car type, mainly Plate ‘J’ and Plate ‘K’, with maximum heights above Top of Rail or 19′-0″ and 20′-3″ respectively. The housing may tend to have gable ends and bridge plates that are movable to an extended position to span the gap between adjacent cars during loading and unloading. Those end closures, when open, permit circus loading of the cars, i.e., sequential loading of the automotive vehicles by driving in one end, and out the other on arrival. Although other kinds of end closures are known, most typically radial arm doors are mounted at the ends and are movable between open and closed positions to govern loading and unloading of the cars. The racks are typically replaced twice during the economic life of the autorack car underframe. That is, the old rack is removed from the underframe and replaced with a new set of racks.
Racks have doors. They may be folding doors, as shown and described herein. The folding doors may have two or more panels that are connected together in a hinged relationship permitting mutual angular deflection during door opening and closing. The panels of the door may tend to be rather long, and may tend to be prone to vibrate. One particular mode of vibration that may be observed is longitudinal vibration (i.e., the excursion is in the rolling direction of the car), at the lowest natural frequency of the panel.
It may be that the doors have access fittings, such as ladders or rungs defining ladders, mounted thereto for the purpose of permitting railroad personnel to ascend the various decks. It may also be that under certain operating conditions it may be desirable to have those access fittings in one configuration, such as a withdrawn, retracted, or stowed condition, while under other operating conditions it may be desirable for those fittings to be in a deployed or extended configuration.